CIB3 (calcium and integrin binding family member 3) is an auxiliary subunit of the mechanotransduction (MET) channel in hair cells, functioning alongside its homolog CIB2 in sensory processes 1. CIB3 contains canonical EF-hand motifs that enable calcium and magnesium ion binding, which induces conformational changes exposing hydrophobic surface areas critical for protein interactions 2. Mechanistically, CIB3 binds to transmembrane channel-like proteins (TMC1/2) through a conserved hydrophobic groove, regulating their localization and function in hair cells—a mechanism structurally similar to auxiliary subunits of voltage-gated Kv4 channels 1. Functionally, CIB3 can substitute for CIB2 in cochlear hair cells, and both proteins work jointly to regulate balance 3. Calcium modulates CIB3's interaction with TMC1 at multiple binding sites, functioning as a calcium sensor in MET channel regulation 4. Disease relevance is demonstrated by mutations in CIB genes causing hearing loss and balance disorders, with pathogenic CIB2/3 variants showing diminished calcium-binding affinities and altered TMC1 interactions 4. Additionally, CIB3 was identified through genome-wide association studies as a candidate gene associated with psychological resilience 5. Double knockout of Cib2 and Cib3 produces circling behavior in mice, highlighting the critical importance of these proteins in vestibular function 6.